Truncation of the GABA(A)-receptor gamma2 subunit in a family with generalized epilepsy with febrile seizures plus - PubMed (original) (raw)

doi: 10.1086/338710. Epub 2001 Dec 17.

David N Bowser, Leanne M Dibbens, Rita Singh, Fiona Phillips, Robyn H Wallace, Michaella C Richards, David A Williams, John C Mulley, Samuel F Berkovic, Ingrid E Scheffer, Steven Petrou

Affiliations

Truncation of the GABA(A)-receptor gamma2 subunit in a family with generalized epilepsy with febrile seizures plus

Louise A Harkin et al. Am J Hum Genet. 2002 Feb.

Abstract

Recent findings from studies of two families have shown that mutations in the GABA(A)-receptor gamma2 subunit are associated with generalized epilepsies and febrile seizures. Here we describe a family that has generalized epilepsy with febrile seizures plus (GEFS(+)), including an individual with severe myoclonic epilepsy of infancy, in whom a third GABA(A)-receptor gamma2-subunit mutation was found. This mutation lies in the intracellular loop between the third and fourth transmembrane domains of the GABA(A)-receptor gamma2 subunit and introduces a premature stop codon at Q351 in the mature protein. GABA sensitivity in Xenopus laevis oocytes expressing the mutant gamma2(Q351X) subunit is completely abolished, and fluorescent-microscopy studies have shown that receptors containing GFP-labeled gamma2(Q351X) protein are retained in the lumen of the endoplasmic reticulum. This finding reinforces the involvement of GABA(A) receptors in epilepsy.

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Figures

Figure 1

Figure 1

Pedigree of an Australian family with GEFS+. An asterisk (*) indicates members carrying the Q351X mutation in GABRG2, and a minus sign (−) indicates members who were tested and are negative for the Q351X mutation.

Figure 2

Figure 2

Sequencing trace of a portion of exon 9 GABRG2, showing the c.1168C→T transition (arrow). The upper chromatogram shows the mutation, and the lower chromatogram shows the control sequence.

Figure 3

Figure 3

Schematic representation of the GABRG2 protein, with arrows indicating the positions of mutations associated with epilepsy.

Figure 4

Figure 4

Two-electrode voltage-clamp recordings in oocytes, demonstrating that coexpression of the GABRG2Q351X abolishes the response to GABA. For all recordings,

_n_=6

. The current and time scale bars apply to all traces. Holding potential was −80 mV. A, Injection of oocytes with wild-type GABRA1:GABRB2:GABRG2 cRNAs (1:1:10 ratio, to favor assembly of γ subunit–containing complexes), resulting in both a robust inward current response to GABA and a low sensitivity to Zn2+ blockade, characteristic of GABRG2 coexpression. B, Expression of GABRA1:GABRB2 only (1:1 ratio). This also produced robust responses to GABA, but with high sensitivity to blockade by Zn2+. C, Expression of GABRA1:GABRB2:GABRG2Q351X subunits (1:1:10 ratio), abolishing GABA-induced currents.

Figure 5

Figure 5

Imaging of GFP-tagged GABRG2 expressed with GABRA1 and GABRB2 subunits, revealing the fate of GABRG2Q351X-containing receptors in HEK293 cells. Images were obtained by confocal fluorescence microscopy (excitation, 488 nm; emission, >515 nm). The scale bar in panel C corresponds to 5 microns and applies to all three panels. A, EGFP-tagged wild-type GABRG2 subunit, found in both the membrane and the intracellular compartment (

_n_=20

individual cells analyzed). B, EGFP-tagged GABRG2Q351X, found only in the intracellular compartment (

_n_=20

individual cells analyzed). C, ER-targeted EYFP expression, demonstrating subcellular distribution of ER that is remarkably similar to that seen in B.

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References

Electronic-Database Information

    1. GenBank, http://www.ncbi.nlm.nih.gov/Genbank/ (for human GABRG2 cDNA reference sequence [accession number nm_000816])
    1. Online Mendelian Inheritance in Man (OMIM), http://www.ncbi.nlm.nih.gov/Omim/ (for GEFS+ [MIM <604233>]) - PubMed

References

    1. Alekov AK, Rahman MM, Mitrovic N, Lehmann-Horn F, Lerche H (2001) Enhanced inactivation and acceleration of activation of the sodium channel associated with epilepsy in man. Eur J Neurosci 13:2171–2176 - PubMed
    1. Barnard EA, Skolnick P, Olsen RW, Mohler H, Sieghart W, Biggio G, Braestrup C, Bateson AN, Langer SZ (1998) International Union of Pharmacology. XV. Subtypes of γ-aminobutyric acidA receptors: classification on the basis of subunit structure and receptor function. Pharmacol Rev 50:291–313 - PubMed
    1. Baulac S, Huberfeld G, Gourfinkel-An I, Mitropoulou G, Beranger A, Prud’homme J-F, Baulac M, Brice A, Bruzzone R, LeGuern E (2001) First evidence of GABAA receptor dysfunction in epilepsy: a mutation in the γ2-subunit gene. Nat Genet 28:46–48 - PubMed
    1. Claes L, Del-Favero J, Ceulemans B, Lagae L, Van Broeckhoven C, De Jonghe P (2001) De novo mutations in the sodium-channel gene SCN1A cause severe myoclonic epilepsy of infancy. Am J Hum Genet 68:1327–1332 - PMC - PubMed
    1. Connolly CN, Krishek BJ, McDonald BJ, Smart TG, Moss SJ (1996) Assembly and cell surface expression of heteromeric and homomeric gamma-aminobutyric acid type A receptors. J Biol Chem 271:89–96 - PubMed

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